A multi axis space phasor based current hysteresis controller for PWM inverters

In conventional three-phase current hysteresis controllers, the current error along the three phase axes are independently controlled. This will result in random selection of switching vectors causing high inverter switching losses. In this paper, a space phasor based multi axis current hysteresis controller is proposed, in which the current error along the orthogonal axes (jA, jB, jC) are monitored. The current error boundary is a hexagon. The proposed control scheme can be implemented using simple look up tables. The advantages of the proposed current hysteresis controlled PWM scheme, when compared to other multi level current hysteresis controllers, is that only the adjacent vectors close to the motor back EMF space phasor voltage, is only used for the inverter switching, for the entire speed range (optimum PWM switching). In the present scheme, the selection of the inverter voltage vectors for optimum PWM switching is achieved without any computation of the machine voltage space phasor, for the full speed range of the drive system. The proposed scheme is self-adapting, as far as the motor space phasor voltage is concerned, and also maintains the controller simplicity and quick response features of a hysteresis current controller. The scheme is simulated and also experimentally verified.